The agreement is widely viewed as a major breakthrough that provides a glimmer of hope after nearly a decade of crisis.

But the deal is, after all, a temporary one, and is by no means seen as a guarantee of long-term success. All parties to the talks now face intense scrutiny on every point they hammered out in Geneva and must win over hard-liners both at home and abroad. For the United States, that includes key allies Saudi Arabia and Israel, which has already rejected the deal.

Vali Nasr, the dean of the School of Advanced International Studies at Johns Hopkins University and a former State Department foreign-policy expert, believes relations with Iran have entered uncharted territory.

"The Iranian regime, which has always defined itself against the United States and has rejected participating in the international system as defined by the United States, has formally and publicly entered into an agreement with the United States," Nasr says, "so they have crossed a line that they had not crossed before."

Tricky First Step

The deal, which lasts for six months, freezes or reverses progress on Tehran's most contentious nuclear work in return for limited sanctions relief.

Over the next six months Iran will gain access to about $3.6 billion of its frozen foreign-reserve holdings. In addition, restrictions affecting Iran's trade in petrochemical products, gold, and airplane and automobile parts will be eased. In total, the relief package is believed to amount to roughly $7 billion.

Iran will be allowed to continue to enrich uranium, but only to a low-grade level of 5 percent. Its current stockpile of near 20 percent-enriched uranium will have to be eliminated or diluted, and new low-grade material cannot exceed current stockpile levels.

Tehran must stop installing new centrifuges to enrich uranium and must end work on thousands of others that are not yet functioning.

Furthermore, Iran has agreed to stop all construction activity at its Arak heavy-water nuclear reactor, which could be used to produce plutonium.

To ensure that all these requirements are being met, Iran has agreed to allow daily inspections and video monitoring of its Natanz and Fordow nuclear facilities.

Nasr says each side must be prepared to make more concessions for a lasting agreement to be worked out.

"I think there's still a lack of trust, and a permanent deal would require a lot more ability on both sides to be able to be flexible and compromise -- I don't think we are quite there," Nasr says. "Within Iran, there was a great deal of desire for some relaxation of sanctions, and I think that can be satisfied more easily; but a permanent deal would require a lot more concessions from Iran, and that's a different calculation."

Mark Hibbs, a senior associate of the Nuclear Policy Program at the Bonn-based Carnegie Endowment for International Peace, says U.S. President Barack Obama now has "a delicate balancing act to perform."

"There's Israel and the [Persian] Gulf states to consider, but on the whole this development is as much a major opportunity for the U.S. as it is a challenge," Hibbs says." Noting the calls for some in Congress to impose new sanctions to bring Tehran to heel in negotiations, he says that "it will be up to the U.S. Congress to give the president the freedom to take advantage of it."

...Or Building Block?

But at the end of the day, says Karim Sadjadpour, an Iran expert at the Carnegie Endowment for International Peace, the accord gives Obama room to maneuver. "It helps ensure Obama's two overarching goals vis-a-vis Iran -- don't allow them to get the bomb, and don't bomb them," he says.

Ali Vaez, a senior Iran analyst at the International Crisis Group, concurs, saying there is now separation between Iran’s peaceful and potential military nuclear capabilities. This, he says, virtually eliminates the possibility of Iran dashing to assemble a nuclear weapon without prompt detection and response by the international community.

"Like hurdling track and field, springing over the first obstacle does not guarantee victory," he says. "But without it the race is lost."

Hibbs says both sides have bought six months to deflate tensions and build some trust, although, he notes, that is not a lot of time.

"Iran for the first time in a decade has agreed to suspend the most provocative of its nuclear activities," Hibbs says. "And if both sides can figure out how to match Iranian cooperation with sanctions-lifting, the two sides can create enough space to settle the longer-term issues at the end of the tunnel: how much enrichment, the future of the Arak project, long-term [International Atomic Energy Agency] verification."